Apparatus and method for detecting wobble signal read from optical disc

ABSTRACT

An apparatus and method for detecting a wobble signal read from an optical disc. The wobble signal detection apparatus comprises an analog/digital (A/D) converter for A/D-converting an analog wobble signal, read from the optical disc and then band pass filtered, a slope detector for detecting a slope of the A/D-converted wobble signal according to a variation thereof, and a wobble signal detector for detecting a peak point of the A/D-converted wobble signal using the detected wobble signal slope, and detecting/outputting a square-wave wobble signal with a high level or low level transition at the detected peak point. The slope detector calculates variations of data values of the A/D-converted wobble signal sampled within a predetermined period on the basis of predetermined different weights, accumulates the calculated values and detects the slope of the A/D-converted wobble signal on the basis of the accumulated value. The predetermined period is an interval where at least two wobble signal data samples are obtained. Therefore, a stable wobble signal can be detected even though a low-frequency fluctuation component and DC offset component are introduced into the analog wobble signal read from the optical disc or the analog wobble signal varies in amplitude.

[0001] This application is a Continuation of co-pending application Ser.No. 10/294,818, filed on Nov. 15, 2002, and for which priority isclaimed under 35 U.S.C. § 120; and this application claims priority ofApplication Nos. 2001-0071611 filed in Korea on Nov. 17, 2001, and2001-0079074 filed in Korea on Dec. 13, 2001, under 35 U.S.C. § 119; theentire contents of all are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to an apparatus and method fordetecting a wobble signal read from an optical disc such as a writablecompact disc (CD) or digital versatile disc (DVD).

[0004] 2. Description of the Related Art

[0005] It is common that a writable optical disc, such as a digitalversatile disc-random access memory (DVD-RAM) or digital versatiledisc-re-writable (DVD-RW), has grooves formed along spiral or concentrictracks. Here, portions of the optical disc other than the grooves aretypically called lands. Data can be recorded on only any one or both ofeach groove and each land according to a writing method. A specificvariation is applied to a wall of each groove in a groove formationprocess, and a specific frequency signal is generated based on thespecific variation in a recording/reproduction process, so it can beused as auxiliary clock means. Here, the specific variation is called awobble and the specific frequency signal is called a wobble signal.

[0006]FIG. 1 shows the construction of a conventional apparatus fordetecting a wobble signal read from an optical disc. As shown in thisdrawing, the conventional wobble signal detection apparatus comprises aband pass filter (BPF) 10 for filtering a push-pull signal, or an analogwobble signal, read from a writable optical disc, for example, a DVD-RWat a predetermined frequency band to remove a high-frequency noisecomponent, a direct current (DC) offset component, etc. therefrom. Ananalog/digital (A/D) converter (ADC) 11 is provided to A/D-convert anoutput analog wobble signal of the predetermined frequency band from theband pass filter 10 to output a digital wobble signal. A wobble signaldetector 12 acts to slice the A/D-converted digital wobble signal on thebasis of a predetermined reference level, for example, a zero level todetect/output a square-wave wobble signal. A wobble phase locked loop(PLL) 100 is provided to output a wobble PLL clock synchronized with thesquare-wave wobble signal. FIG. 2 shows measured waveforms of thefiltered wobble signal from the band pass filter 10, the sliced wobblesignal from the wobble signal detector 12 and the PLL clock from thewobble phase locked loop 100.

[0007] The conventional wobble signal detection apparatus furthercomprises a bit detector 16 for detecting/converting the square-wavewobble signal into a stream of bits having values of 1 or 0, using thewobble PLL clock. A synchronous (Sync) detector 17 acts to detect asynchronous pattern placed in the square-wave wobble signal from the bitstream and generate and output a synchronous signal corresponding to thedetected synchronous pattern. An address decoder 18 is provided todecode a physical address of the optical disc from the bit stream on thebasis of the synchronous signal.

[0008] The wobble PLL 100 includes a phase error detector 13 fordetecting a phase error at a point of time that the A/D-converted wobblesignal crosses a zero point from positive to negative, namely, anegative zero crossing point (referred to hereinafter as ‘NZCP’) asshown in FIG. 3. A time count value that determines an oscillatingfrequency of a digital controlled oscillator (DCO) 15 in the wobble PLL100, for example, a free down time count value, is always corrected withthe phase error detected at the NZCP.

[0009] At this time, in a case (lead case) where the phase of the PLLclock, which is generated by the digital controlled oscillator 15, isahead of that of the A/D-converted wobble signal, the phase errordetector 13 detects/generates a positive phase error as shown in FIG. 3and outputs the generated phase error to a loop filter 14 in the wobblePLL 100. The loop filter 14 then corrects a time count value fordetermination of a clock frequency of the digital controlled oscillator15 into a smaller value according to the positive phase error.

[0010] On the other hand, in a case (lag case) where the phase of thePLL clock generated by the digital controlled oscillator 15 is behindthat of the A/D-converted wobble signal, the phase error detector 13detects/generates a negative phase error as shown in FIG. 3 and outputsthe generated phase error to the loop filter 14, which then corrects thetime count for determination of the clock frequency of the digitalcontrolled oscillator 15 into a larger value according to the negativephase error.

[0011] As a result, the wobble PLL 100 continuously performs a phaseerror correction operation for synchronization of the PLL clock with thewobble signal by detecting a phase error at the NZCP and correcting thetime count for determination of the clock frequency of the digitalcontrolled oscillator 15 on the basis of the detected phase error.

[0012] However, recently, as the optical disc becomes higher inrecording density, recording tracks thereof have denser pitches,resulting in a greater crosstalk effect caused by a wobble signal of anadjacent track. This greater crosstalk effect makes the output wobblesignal from the band pass filter 10 very small in signal to noise (S/N)ratio, so a stable wobble signal cannot be detected by the conventionalwobble signal detection apparatus.

[0013] In addition, provided that a tracking servo and focusing servoare unstable or a surface vibration of the optical disc, etc. occur, alow-frequency fluctuation component and DC offset component will beintroduced into the output wobble signal from the band pass filter 10 orthe wobble signal will vary in amplitude. For example, as shown in FIG.4, in the case {circle over (1)} where a stable wobble signal with aconstant amplitude is outputted from the band pass filter 10, a stablewobble signal {circle over (4)} is normally detected by the wobblesignal detector 12. Alternatively, in the case {circle over (2)} where alow-frequency fluctuation component and DC offset component arecontained in the output wobble signal from the band pass filter 10, orin the case {circle over (3)} where the output wobble signal from theband pass filter 10 has a varying amplitude and DC offset component, anabnormal wobble signal {circle over (5)} or {circle over (6)} isdetected by the wobble signal detector 12. Consequently, the wobblephase locked loop cannot normally perform the phase error correctionoperation.

SUMMARY OF THE INVENTION

[0014] Therefore, the present invention has been made in view of theabove problems, and it is an object of the present invention to providean apparatus and method for detecting a stable wobble signal even thougha low-frequency fluctuation component and DC offset component areintroduced into an analog wobble signal read from an optical disc or theanalog wobble signal varies in amplitude.

[0015] In accordance with one aspect of the present invention, the aboveand other objects can be accomplished by the provision of a wobblesignal detection apparatus comprising analog/digital (A/D) conversionmeans for A/D-converting an analog wobble signal, read from an opticaldisc and then band pass filtered; slope detection means for detecting aslope of the A/D-converted wobble signal according to a variationthereof; and wobble signal detection means for detecting a peak point ofthe A/D-converted wobble signal using the detected wobble signal slope,and detecting/outputting a square-wave wobble signal with a high levelor low level transition at the detected peak point; the slope detectionmeans calculating variations of data values of the A/D-converted wobblesignal sampled within a predetermined period on the basis ofpredetermined different weights, accumulating the calculated values anddetecting the slope of the A/D-converted wobble signal on the basis ofthe accumulated value, the predetermined period being an interval whereat least two wobble signal data samples are obtained.

[0016] In accordance with another aspect of the present invention, thereis provided a wobble signal detection method comprising the steps of a)band pass filtering and A/D-converting an analog wobble signal read froman optical disc, and detecting a slope of the A/D-converted wobblesignal; b) detecting a peak point of the A/D-converted wobble signalusing the detected wobble signal slope; and c) detecting/outputting asquare-wave wobble signal with a high level or low level transition atthe detected peak point; the step a) of detecting the wobble signalslope including the step of comparing data values of the A/D-convertedwobble signal sampled within a predetermined period with an arbitraryreference wobble signal data value, respectively, obtaining therespective differences as a result of the comparisons, multiplying theobtained differences by different weights, respectively, accumulatingthe multiplied values, comparing the accumulated value with apredetermined threshold value, and detecting the wobble signal slope inaccordance with the compared result.

[0017] In accordance with a further aspect of the present invention,there is provided a wobble signal detection method comprising the stepsof a) band pass filtering an analog wobble signal read from an opticaldisc, and A/D-converting the filtered wobble signal into a digitalwobble signal; b) detecting a peak point of the A/D-converted digitalwobble signal; c) determining whether a counted value obtained byfrequency-counting an interval between the detected wobble signal peakpoint and a just previously detected wobble signal peak pointcorresponds to a bit length of an integer multiple of 3; and d)initializing the counted value if it corresponds to the bit length ofthe integer multiple of 3, performing a re-counting operation, anddetecting/outputting a square-wave wobble signal with a high level orlow level transition at a point of time that a re-counted valuecorresponds to a desired bit length.

[0018] In accordance with yet another aspect of the present invention,there is provided a wobble signal detection apparatus comprising A/Dconversion means for A/D-converting an analog wobble signal, read froman optical disc and then band pass filtered; slope detection means fordetecting a slope of the A/D-converted wobble signal according to avariation thereof; peak detection means for detecting a peak point ofthe A/D-converted wobble signal using the detected wobble signal slope;counting means for frequency-counting an interval between the detectedwobble signal peak point and a just previously detected wobble signalpeak point; and level transition means for, if a counted value obtainedby frequency-counting the interval between the detected wobble signalpeak point and the just previously detected wobble signal peak pointcorresponds to a bit length of an integer multiple of 3, initializingthe counted value, and making a high level or low level transition at apoint of time that a re-counted value corresponds to a desired bitlength.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The above and other objects, features and other advantages of thepresent invention will be more clearly understood from the followingdetailed description taken in conjunction with the accompanyingdrawings, in which:

[0020]FIG. 1 is a block diagram showing the construction of aconventional apparatus for detecting a wobble signal read from anoptical disc;

[0021]FIG. 2 is a waveform diagram of signals detected by theconventional apparatus of FIG. 1;

[0022]FIG. 3 is a waveform diagram of a phase error, PLL clock anddigital controlled oscillator time count in a wobble PLL in FIG. 1;

[0023]FIG. 4 is a waveform diagram of wobble signals abnormally detectedby a wobble signal detector in FIG. 1;

[0024]FIG. 5 is a block diagram showing the construction of an apparatusfor detecting a wobble signal read from an optical disc in accordancewith a preferred embodiment of the present invention;

[0025]FIG. 6 is a waveform diagram illustrating a wobble signal slopedetection process in accordance with the embodiment of the presentinvention;

[0026]FIG. 7 is a waveform diagram of wobble signal slope detectionsignals in accordance with the embodiment of the present invention;

[0027]FIG. 8 is a waveform diagram illustrating a wobble signal peakdetection process in accordance with the embodiment of the presentinvention;

[0028]FIG. 9 is a waveform diagram of a wobble signal peak detectionsignal in accordance with the embodiment of the present invention;

[0029]FIG. 10 is a waveform diagram of wobble signals normally detectedby the wobble signal detection apparatus and method in accordance withthe embodiment of the present invention;

[0030]FIG. 11 is a waveform diagram illustrating a state where ahigh-frequency noise component is contained in a wobble signal inputtedto a slope detector in accordance with the embodiment of the presentinvention;

[0031]FIG. 12 is a waveform diagram illustrating a different example ofthe wobble signal slope detection process in accordance with theembodiment of the present invention;

[0032]FIG. 13 is a waveform diagram of wobble signal slope detectionsignals generated according to the example of FIG. 12;

[0033]FIG. 14 is a block diagram showing the construction of anapparatus for detecting a wobble signal read from an optical disc inaccordance with an alternative embodiment of the present invention;

[0034]FIG. 15 is a detailed block diagram of a wobble signal detector inFIG. 14;

[0035]FIG. 16 is a waveform diagram of wobble signals detected by thewobble signal detection apparatus in accordance with the secondembodiment of the present invention;

[0036]FIG. 17 is a flow chart illustrating a wobble signal detectionmethod in accordance with the second embodiment of the presentinvention;

[0037]FIG. 18 is a waveform diagram illustrating a process of detectinga wobble signal with a level transition in the wobble signal detectionmethod in accordance with the second embodiment of the presentinvention; and

[0038]FIG. 19 is a waveform diagram illustrating the comparison betweena wobble signal detected by the wobble signal detection method inaccordance with the second embodiment of the present invention andwobble signals abnormally detected by conventional wobble signaldetection methods.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0039] With reference to FIG. 5, there is shown in block form theconstruction of an apparatus for detecting a wobble signal read from anoptical disc in accordance with a preferred embodiment of the presentinvention.

[0040] As shown in FIG. 5, the wobble signal detection apparatuscomprises a slope detector 21 for detecting a positive slope andnegative slope of a wobble signal, A/D-converted as stated previouslywith reference to FIG. 1, and a wobble signal detector 22 fordetecting/deciding a peak point of the A/D-converted wobble signal onthe basis of the positive slope and negative slope anddetecting/outputting a square-wave wobble signal with a high level orlow level transition at the decided peak point.

[0041] The wobble signal detection apparatus further comprises a wobblePLL 200 including a phase error detector 23, loop filter 24 and digitalcontrolled oscillator 25. The phase error detector 23compares/calculates a phase error between an output PLL clock from thedigital controlled oscillator 25 and the square-wave wobble signal withthe level transition at the peak point. The loop filter 24 filters anoutput phase error value from the phase error detector 23 to generate aphase correction value. The digital controlled oscillator 25 corrects acurrent PLL clock oscillating frequency according to the phasecorrection value generated by the loop filter 24 to output the PLLclock.

[0042] The PLL clock generated and outputted by the wobble PLL 200 isalso applied to the bit detector 16 to which the A/D-converted wobblesignal is inputted. The bit detector 16 detects/converts theA/D-converted wobble signal into a stream of bits having values of 1 or0, using the PLL clock. The synchronous detector 17 detects asynchronous pattern placed in the A/D-converted wobble signal from thebit stream and generates and outputs a synchronous signal correspondingto the detected synchronous pattern. The address decoder 18 decodes aphysical address of the optical disc from the bit stream from the bitdetector 16 on the basis of the synchronous signal from the synchronousdetector 17.

[0043] A detailed description will hereinafter be given of the wobblesignal detection operation performed by the slope detector 21 and wobblesignal detector 22.

[0044]FIG. 6 is a waveform diagram illustrating a wobble signal slopedetection process in accordance with the embodiment of the presentinvention, and FIG. 7 is a waveform diagram of wobble signal slopedetection signals in accordance with the embodiment of the presentinvention. As shown in FIG. 6, an output analog wobble signal from theband pass filter 10 is A/D-converted by the A/D converter 11 and theninputted to the slope detector 21. In order to remove a high-frequencynoise component mixed in the A/D-converted wobble signal, the slopedetector 21 compares a value of the currently A/D-converted digitalwobble signal data with that of digital wobble signal data A/D-convertedbefore a predetermined period of time (for example, 10% of a wobblesignal period), not the just previously A/D-converted digital wobblesignal data, to obtain a difference between the two values. The slopedetector 21 then detects a slope of the wobble signal if the obtaineddifference is greater than or equal to a predetermined threshold value,for example, 2 bits. For example, assume that 70 wobble signal datasamples are obtained during one wobble signal period, as shown in FIG.6. In this case, if the currently A/D-converted digital wobble signaldata is ‘1101 10XX’ (XX are ignored) and digital wobble signal datasampled before 10% of the wobble signal period, namely, wobble signaldata sampled before 7 samples is ‘1111 01XX’ (XX are ignored), thecompared result (1101 10XX−1111 01XX) is a negative (−) value indicativeof a difference of 2 or more bits. As a result, the slope detector 21detects a negative slope of the wobble signal. To the contrary, in thecase where the compared result is a positive (+) value indicative of adifference of 2 or more bits, the slope detector 21 detects a positiveslope of the wobble signal. Accordingly, the slope detector 21detects/outputs, as shown in FIG. 6, a negative slope detection signalwhich becomes high in level when the compared result is a negative (−)value, and a positive slope detection signal which becomes high in levelwhen the compared result is a positive (+) value, respectively.

[0045] Hence, the positive slope detection signal and the negative slopedetection signal inputted to the wobble signal detector 22 havedifferent waveforms as shown in FIG. 7.

[0046]FIG. 8 is a waveform diagram illustrating a wobble signal peakdetection process in accordance with the embodiment of the presentinvention, and FIG. 9 is a waveform diagram of a wobble signal peakdetection signal in accordance with the embodiment of the presentinvention.

[0047] Upon receiving the positive slope detection signal and negativeslope detection signal as stated above, the wobble signal detector 22creates a virtual window having a certain length, and accumulatespositive slope values and negative slope values existing within thecreated window, respectively. The length of the window is preferably setto ½ (T/2) of one wobble signal period (1T).

[0048] Then, the wobble signal detector 22 compares the accumulatedpositive slope value and the accumulated negative slope value with eachother, and outputs a high signal if the accumulated positive slope valueis greater than the accumulated negative slope value and a low signal ifthe accumulated positive slope value is not greater than the accumulatednegative slope value.

[0049] As a result, the wobble signal detector 22 detects/decides a peakpoint of the analog wobble signal in response to the positive slopedetection signal and negative slope detection signal and outputs asquare-wave wobble signal with a high level or low level transition atthe decided peak point. The analog wobble signal, the positive slope,the negative slope, and the wobble signal outputted from the wobblesignal detector have waveforms as shown in FIG. 9, respectively.

[0050] Therefore, in accordance with the preferred embodiment of thepresent invention, as shown in FIG. 10, in the case {circle over (1)}′where a stable wobble signal with a constant amplitude is outputted fromthe band pass filter, a stable wobble signal {circle over (2)}′ with alevel transition at a peak point of the output wobble signal from theband pass filter is normally detected by the wobble signal detector 22.Further, even in the case {circle over (3)}′ where a low-frequencyfluctuation component and DC offset component are contained in theoutput wobble signal from the band pass filter, or in the case {circleover (5)}′ where the output wobble signal from the band pass filter hasa varying amplitude and DC offset component, a stable wobble signal{circle over (4)}′ or {circle over (6)}′ with a level transition at apeak point of the output wobble signal from the band pass filter isdetected/outputted by the wobble signal detector 22.

[0051] On the other hand, in the case where a notch-shaped orspark-shaped high-frequency noise component is contained in the filteredanalog wobble signal from the band pass filter 10, a slope detectionerror of the wobble signal may occur due to the high-frequency noisecomponent. A slope detection method for preventing such a slopedetection error will hereinafter be described in detail with referenceto the annexed drawings.

[0052] As shown in FIG. 11, in the case where a high-frequency noisecomponent is introduced into an analog wobble signal (indicated by adotted line), it is filtered by the band pass filter 10 and theninputted as a wobble signal (indicated by a solid line) with anotch-shaped or spark-shaped high-frequency noise component to the A/Dconverter 11.

[0053] As a result, wobble signal data sampled and A/D-converted by theA/D converter 11 has values irregularly incremented and decremented dueto the notch-shaped or spark-shaped noise component. For example, asshown in FIG. 11, in a case (good sampling case) where wobble signaldata values obtained by sampling the wobble signal with thehigh-frequency noise component are X(0)˜X(n), wobble signal datacorresponding to the original wobble signal is normally outputted to theslope detector 21. However, in a case (bad sampling case) where wobblesignal data values obtained by sampling the wobble signal with thenotch-shaped or spark-shaped high-frequency noise component are X′(0)˜X′ (n), wobble signal data different from the original wobble signalis outputted to the slope detector 21.

[0054] In other words, as shown in an interval ‘A’ in FIG. 11, the(n+2)th sampled wobble signal data value X′ (1) is larger than the(n+3)th sampled wobble signal data value X′ (2). As a result, when aslope is determined on the basis of the comparison between the wobblesignal data values at the two points, the slope is erroneously detectedas a slope where the wobble signal decreases, although the originalwobble signal increases.

[0055] Therefore, the slope detector 21, as shown in FIG. 12, creates awindow having a certain interval, for example, an interval where 11wobble signal data values X(0)˜X(10) are sampled, sets the first wobblesignal data value X(0) sampled within the created window as a referencewobble signal data value, compares the set reference wobble signal datavalue with each of the subsequent wobble signal data values X(1)˜X(10)sequentially sampled within the window, obtains the respectivedifferences as a result of the comparisons, and multiplies the obtaineddifferences by different weights W(1)˜W(10), respectively.

[0056] Then, the slope detector 21 accumulates all values obtained bymultiplying the differences, respectively, by the different weightsW(1)˜W(10), compares the accumulated value with a predetermined positivethreshold value for positive slope detection and a predeterminednegative threshold value for negative slope detection, respectively, anddetects/outputs a positive slope and negative slope of the wobble signalwithin the window in accordance with the compared results.

[0057] The weights W(1)˜W(10) are preferably preset to values (W(1)<W(2). . . W(9)<W(10)) which increase in proportion to time differences orspaced distances between the reference wobble signal data value X(0)first sampled within the window and the subsequent wobble signal datavalues X(1)˜X(10) sequentially sampled within the window.

[0058] If a wobble signal slope is detected within a given window Window1, then the above wobble signal slope detection process shifts to a nextwindow Window 2, as shown in FIG. 12.

[0059] Accordingly, the slope detector 21 repeats a sequence ofoperations of setting the first wobble signal data value X(1) sampledwithin the shifted window Window 2 as a reference wobble signal datavalue, comparing the set reference wobble signal data value with each ofthe subsequent wobble signal data values X(2)˜X(11) sequentially sampledwithin the shifted window, obtaining the respective differences as aresult of the comparisons, and multiplying the obtained differences bydifferent weights, respectively, as expressed by the following equation:$\begin{matrix}{{{Sp}(k)} = \begin{matrix}{\sum\limits_{i = 1}^{N}\left\{ {\left\lbrack {{{x(i)} - {X(0)}} > 0} \right\rbrack?} \right.} & \left. \quad {{w(i)}\text{:}0} \right\}\end{matrix}} \\{{{Sn}(k)} = \begin{matrix}{\sum\limits_{i = 1}^{N}\left\{ {\left\lbrack {{{x(i)} - {X(0)}} > 0} \right\rbrack?} \right.} & \left. {{- {w(i)}}\text{:}0} \right\}\end{matrix}} \\{{y(k)} = {{{Sp}(k)} + {{Sn}(k)}}}\end{matrix}\quad$

$\begin{matrix}\begin{matrix}{{if}\quad {\left( {{y(k)} < {Nth}} \right)?}} \\{{else}\quad {if}\quad {\left( {{Nth} < {y(k)} < {Pth}} \right)?}} \\{{else}\quad {if}\quad {\left( {{Pth} < {y(k)}} \right)?}}\end{matrix} & \begin{matrix}{{{Slope}(k)} = {Negative}} \\{{{Slope}(k)} = {Zero}} \\{{{Slope}(k)} = {Positive}}\end{matrix}\end{matrix}\quad$

[0060] Here, N is the size of data to be accumulated, X(n) is sampleddata, X(0) is sampled reference data, W(n) is a weight to a slope basedon two sampled data, Sp(k) is a value obtained by accumulating positiveslope weights of respective sampled data on the basis of X(0), Sn(k) isa value obtained by accumulating negative slope weights of therespective sampled data on the basis of X(0), Pth is a positivethreshold value, Nth is a negative threshold value, and Slope(n) is aslope at X(0).

[0061] Hence, the positive slope detection signal and negative slopedetection signal detected/outputted by the above-described equation andoperation have stable waveforms with no high-frequency noise componentas shown in FIG. 13, so the wobble signal detector 22 can detect a peakpoint more accurately in the wobble signal peak detection processpreviously stated with reference to FIG. 8. Therefore, even in the casewhere the notch-shaped or spark-shaped high-frequency noise component iscontained in the analog wobble signal, a slope detection error of thewobble signal due to the high-frequency noise component can be preventedfrom occurring.

[0062] The present embodiment has been disclosed for illustrativepurposes, and the slope detector 21, wobble signal detector 22 and phaseerror detector 23 may be integrated to configure a single unit.

[0063]FIG. 14 shows the construction of an apparatus for detecting awobble signal read from an optical disc in accordance with analternative embodiment of the present invention. In this drawing, thesame parts as those in FIG. 1 are denoted by the same reference numeralsand a detailed description thereof will hereinafter be omitted.

[0064] A wobble signal detector 30 in the second embodiment includes, asshown in FIG. 15, a slope detector 31, peak detector 32, leveltransition corrector 33 and frequency counter 34.

[0065] The slope detector 31 detects a slope of a digital wobble signalA/D-converted by the A/D converter 11. The peak detector 32 detects apeak point of the digital wobble signal using the detected wobble signalslope. The frequency counter 34 frequency-counts an interval between thepeak point detected by the peak detector 32 and the just previouslydetected peak point and outputs the counted value to the leveltransition corrector 33. If the counted value is a bit length which isan integer multiple of 2, for example, a 2 T or 4 T length defined in awritable optical disc such as a DVD-RW, the level transition corrector33 makes a high or low level transition based on the wobble signal slopeat the peak point detected by the peak detector 32. In the case wherethe counted value is a bit length which is an integer multiple of 3, forexample, a 3 T length, the level transition corrector 33 resets thecounted value to resume the counting operation of the frequency counter34, and then makes a high or low level transition at a point of timethat the re-counted value becomes a 1T length.

[0066] Therefore, even though the A/D-converted digital wobble signalcontains a low-frequency fluctuation component, a DC offset componentand an amplitude variation, the wobble signal detector 30 can detect astable wobble signal. In particular, the wobble signal detector 30 candetect/output a square-wave wobble signal with a bit length of aninteger multiple of 2 which is capable of making the address decodingeasier.

[0067] For example, as shown in FIG. 16, in the case {circle over (1)}where the digital wobble signal inputted to the wobble signal detector30 is a stable wobble signal with a constant amplitude, the peakdetector 32 in the wobble signal detector 30 detects a peak point of thedigital wobble signal according to a slope variation thereof andnormally detects a stable square-wave wobble signal {circle over (7)} onthe basis of the detected peak point. Further, even in the case {circleover (2)} where a low-frequency fluctuation component and DC offsetcomponent are contained in the digital wobble signal, or in the case{circle over (3)} where the digital wobble signal has a varyingamplitude, the peak detector 32 normally detects a stable square-wavewobble signal {circle over (8)} or {circle over (9)} on the basis of apeak point of the digital wobble signal.

[0068] On the other hand, the level transition corrector 33 receives thesquare-wave wobble signal detected/outputted from the peak detector 32and outputs a square-wave wobble signal with a pulse width of a bitlength of an integer multiple of 2, as will hereinafter be described indetail.

[0069]FIG. 17 is a flow chart illustrating a method for detecting awobble signal read from an optical disc in accordance with the secondembodiment of the present invention.

[0070] First, the wobble signal detector 30 detects a slope of an outputdigital wobble signal from the A/D converter 11 (step S10) andcontinuously performs a peak detection operation of detecting a peakpoint of the digital wobble signal based on the detected slope. If apeak point of the wobble signal is detected (step S11), then the wobblesignal detector 30 checks a value frequency-counted beginning with thepreviously detected peak point (step S12).

[0071] For example, upon detecting a Kth peak point P_(K) by monitoringthe slope of the digital wobble signal, the wobble signal detector 30checks a value frequency-counted beginning with the previously detected(K−1)th peak point P_(K−1).

[0072] In the case where the checked frequency-counted value is a bitlength of an integer multiple of 3, for example, a 3 T length (stepS13), the wobble signal detector 30 resets the counted value and thenresumes the counting operation (step S14). Thereafter, if the re-countedvalue becomes a 1T length (step S15), then the wobble signal detector 30makes a high or low level transition at that time point.

[0073] In other words, in the case where a frequency count increasingfrom the (K−1)th peak point P_(K−1) to the Kth peak point P_(K) has avalue corresponding to the 3 T length, as shown in FIG. 18, the wobblesignal detector 30 generates no trigger point for a level transition,initializes the frequency count to zero, and then performs there-counting operation.

[0074] Thereafter, when the frequency re-count has a value correspondingto the 1T length at the above step S15, the wobble signal detector 30generates a trigger point so as to make a high level transition of a 4 Tlength corresponding to an integer multiple of 2 (step S16). At thistime, the wobble signal detector 30 makes a high level transition whenthe digital wobble signal slope at the Kth peak point P_(K) changes fromnegative to positive. Alternatively, the wobble signal detector 30 makesa low level transition when the digital wobble signal slope at the Kthpeak point P_(K) changes from positive to negative.

[0075] On the other hand, in the case where the checkedfrequency-counted value is a bit length of an integer multiple of 2, forexample, a 2 T or 4 T length at the above step S13, the wobble signaldetector 30 generates a trigger point for a level transition so as tomake a high/low level transition (step S16). Thereafter, the wobblesignal detector 30 resets the frequency-counted value to zero (step S17)and then repeats the above operation according to whether the system isended (step S18).

[0076] Therefore, the wobble signal detector 22 detect/outputs asquare-wave wobble signal with a pulse width of a bit length of aninteger multiple of 2, for example, the 2 T or 4 T length, therebyenabling the address decoder 18 to perform the address decodingoperation in a simpler manner.

[0077] For example, as shown in FIG. 18, when a level transition is madeon the basis of a point of peak detection time, a wobble signal isdetected/outputted in the form of peak data with 2 T, 3 T and 4 Tlengths. In this case, the address decoding operation must be performedat a length of ½ T which is the greatest common factor of 2 T, 3 T and 4T, thereby making the address decoder 18 complicated in construction.However, the wobble signal detector 30 enables the address decoder 18 toperform the address decoding operation at a length of 2 T which is thegreatest common factor of 2 T and 4 T, so the address decoder 18 canbecome simpler in construction.

[0078] As seen from FIG. 19, in the case where a digital wobble signalA/D-converted by the A/D converter 11 has a distorted pattern containinga low-frequency fluctuation component, an amplitude variation, etc., awobble signal (Slice Data Signal) detected/outputted by a conventionalslice detection method is an abnormal square-wave wobble signal whichhas a pulse width of a 2 T or 4 T length, but is discontinuouslyinterrupted due to the amplitude variation, etc. Also, a wobble signal(Peak Data Signal) detected/outputted by a conventional peak detectionmethod is a square-wave wobble signal which is stable regardless of theamplitude variation, etc., but has a pulse width of a 2 T, 3 T or 4 Tlength, thereby complicating the address decoding operation.

[0079] On the other hand, a wobble signal (Corrected Transition DataSignal) detected/outputted by the peak detection & transition correctionmethod according to the second embodiment of the present invention is asquare-wave wobble signal which is stable irrespective of the amplitudevariation, etc. and has a pulse width of the 2 T or 4 T lengthfacilitating the address decoding operation.

[0080] As apparent from the above description, the present inventionprovides an apparatus and method for detecting a stable wobble signaleven though a low-frequency fluctuation component and DC offsetcomponent are introduced into an analog wobble signal read from anoptical disc or the analog wobble signal varies in amplitude. Further,according to the present invention, an address decoder for decoding aphysical address of the optical disc can be made simpler inconstruction.

[0081] Although the preferred embodiments of the present invention havebeen disclosed for illustrative purposes, those skilled in the art willappreciate that various modifications, additions and substitutions arepossible, without departing from the scope and spirit of the inventionas disclosed in the accompanying claims.

What is claimed is:
 1. A wobble signal detection apparatus comprising:analog/digital (A/D) conversion means for A/D-converting an analogwobble signal, read from an optical disc and then band pass filtered;slope detection means for detecting a slope of the A/D-converted wobblesignal according to a variation thereof; and wobble signal detectionmeans for detecting a peak point of said A/D-converted wobble signalusing the detected wobble signal slope, and detecting/outputting asquare-wave wobble signal with a high level or low level transition atthe detected peak point; said slope detection means calculatingvariations of data values of said A/D-converted wobble signal sampledwithin a predetermined period on the basis of predetermined differentweights, accumulating the calculated values and detecting the slope ofsaid A/D-converted wobble signal on the basis of the accumulated value,said predetermined period being an interval where at least two wobblesignal data samples are obtained.